Worm drive for starter motors for internal combustion engines

ABSTRACT

An overrunning clutch connects the start pinion to an axially movable coupling member coupled to the armature-shaft-rotated drive member by an ear that freely engages a longitudinal groove in the drive member, which has an internally threaded sleeve that meshes with the threaded portion of the armature shaft and is turned thereby.

United States Patent Vogel et al.

[ 1 Mar. 7, 1972 [54] WORM DRIVE FOR STARTER MOTORS FOR INTERNAL COMBUSTION ENGINES [72] Inventors: Erich Vogel, Bemhausen; Gunter Ulimann, Schwieberdingen; Gerhard Ptluger, Markgroeningen, all of Germany; Robert Bosch GmbH, Stuttgart, Germany [22] Filed: June 19, 1970 [21] Appl.No.: 47,803

[30] Foreign Application Priority Data June 21, 1969 Germany ..P 19 31 582.3

[52] US. C 74/6 [51] Int. Cl ..F02n 11/00 [58] Field of Search ..74/6, 7 A, 7

may;

[56] References Cited UNITED STATES PATENTS 2,554,445 5/1951 Miller ..74/6 3,140,617 7/1964 Palmer ..74/6

Primary Examiner-Milton Kaufman Attomey-Michael S. Striker ABSTRACT An overrunning clutch connects the start pinion to an axially movable coupling member coupled to the armature-shaftrotated drive member by an ear that freely engages a longitudinal groove in the drive member, which has an internally threaded sleeve that meshes with the threaded portion of the armature shaft and is turned thereby.

9 Claims, 1 Drawing Figure PAIENTEDMAR 71972 3545 20 :2 INVENTORS 7 Erich VOGEL R Gunther ULLMANN Gerhard PFLUGER Mum mu their ATTORNEY WORM DRIVE FOR STARTER MOTORS FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION The invention relates to a worm drive for a starter motor for internal combustion engines.

Worm drives for this purpose frequently have a coupling that is rigid in one direction of rotation, the coupling occurring between the teeth of a coupling member turned by a driver and those of another part associated with the start pinion, which teeth together to form an overrunning clutch. Such drives, because of the rigid coupling, are particularly suited to the transmitting of large torques, as is necessary, for example, when starting high-speed diesel engines with direct fuel injection. The drive, however, is severely stresses by the shock occurring when the teeth of the turn pinion mesh with those of the spur gear of the internal combustion engine, by the peak torques that are transmitted during starting up, and by the forces exerted on the teeth of the overrunning clutch after the engine has started and has accelerated to an r.p.m. greater than that of the armature shaft of the starter motor.

In one known embodiment of this kind of worm drive, the means for ensuring a rigid coupling in rotation between the coupling member and the drive are provided on a surface of the coupling member that faces a sleeve of the driver. This construction has the disadvantage that the aforementioned means, because it is located only a relatively small radial distance from the axis of the armature shaft of the starter motor, is subject to very high forces and therefore quickly wears.

SUMMARY OF THE INVENTION An object of the invention is a heavy duty worm drive that is wear resistant and has a long life, yet is composed of simple parts that are easily assembled together to make the worm drive.

The invention comprises broadly a driven gear on the engine, a driving gear, such as a turn pinion, arranged to be put into and out of mesh with the driven gear, a rotary input shaft, such as an armature shaft, of a starter motor, drive means movable axially of and operatively connected with the input shaft to perform an angular movement in response to axial movement, shifting means for moving the drive means axially, and coupling means comprising a first member radially spaced from the input shaft and provided on the drive means, and a second member coupled to the first member and operatively connected to the driving gear to move the latter angularly and axially into mesh with the driven gear in response to axial movement of the drive means.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a longitudinal view, partly cut away and partly in cross section, of an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The armature, or input, shaft of a starter motor, not shown, is supported at its left end in a bearing plate 11, for rotation. The shaft has a smooth length 12, which supports a turn pinion, or driving gear, 13, free to rotate and to move axially. It also has a length 14 with a coarse thread 15, onto which is screwed a cup-shaped driver 16 having an internally threaded sleeve 17. The driver has at least one longitudinal slot 18 in its circumference, and advantageously has a plurality of such slots uniformly spaced about the circumference. If the slotted circumference of the driver is considered as being the first member of a coupling arrangement, the coupling member 19 constitutes the second member. This latter member, which is free to rotate and to move axially on the shaft 10, has an ear 20, constituting the male element, that freely engages a slot 18, constituting the female element, so that the coupling member 19 can easily move axially on the shaft. The face 21 of the coupling member 19 facing the pinion 13 has saw-toothed coupling teeth 22 that mesh with similar teeth 23, which are incorporated in the face of a flange part 24 of the pinion 13 that projects into the cup-shaped driver 16. A coil spring 26, held in compression between the member 19 and the inner face of the radial wall 25 of the driver 16, presses the teeth 22 and 23 into engagement. These teeth constitute an overrunning clutch, which permits the shaft 13 to rotate relative to the driver I6, when the engine that is to be started has started up and accelerates the pinion 13 with respect to the armature shaft 10 of the starter motor. An elastomeric ring 27 is fixed in any suitable manner to the inner face of the wall 25. The parts 19 and 24 are held inside the cup-shaped driver 16 by a retaining ring 28, which bears against the face 29 of the flange 24 and is held in an internal annular groove in the driver 16.

The sleeve 17 supports a two-piece collar 30, which the forked arm of a starting, or engaging, lever 31 engages. A coil spring 32, which is supported at its left end by the outer face of the radial wall of the driver 16, presses the collar 30 against a retaining ring 33 rigidly held on the sleeve 17. The lever 31 is operated by a starting relay, not shown, and, by means of the spring 32, the driver 16, and the coupling member 19, pushes the pinion 13 into mesh with the spur gear of the internal combustion engine, not shown. The position of the pinion 13 when completely engaged is determined by a stop ring 35 rigidly held on the shaft 10.

The manner of constructing the coupling member 19 and the driver 16 so as to couple them together in rotation, while the member 19 remains completely free to move axially, ensures that the coupling between 16 and 19 occurs at a greater radial spacing from the shaft 10 than is the case in the embodiment of the prior art previously discussed.

When disengaging the teeth 22 and 23, the action of the overrunning clutch is helped by a centrifugal force uncoupler, located between the coupling member 19 and the flange 24 and consisting of a ball race 36, at least two uniformly spaced balls 37 in the race, and a conical ring 38. The race 36 is securely held in an annular recess 39 of the flange 24. The conical ring 38 is fixed to the face 21 of the member 19, and its conical surface 40 rests on the balls 37. These parts are so dimensioned that even when the overrunning clutch is completely engaged the balls 37 are held with virtually no axial play between the ball race 36 and the conical ring 38.

In operation, the electromagnetically operated starting lever 31 pushes the collar 30, the driver 16, the coupling member 19, and the turn pinion 13 towards the spur gear 34. If the teeth of the pinion and the spur gear are positioned so as to permit their meshing, the engaging movement is continued until the pinion reaches the stop ring 35. At this moment a starter switch, not shown, is closed in the usual manner, and the starter motor is turned on. The armature shaft is set into rotation, and the driver 16 is screwed along the coarse thread 15 towards the spur gear 34. By means of the elastomeric ring 27 and the coupling member 19 it presses the pinion 13 against the ring stop 35. The internal combustion engine is turned over by the pinion 13, which, in turn, is rotated by the shaft 10 acting through the driver 16, the coupling member 19, and the teeth 22 and 23, which are held in positive engagement in the direction of rotation.

The elastomeric ring 27 largely reduces the shock that occurs when the driver 16 strikes the coupling member 19, and the pinion 13, which is in mesh with the spur gear 34, starts up. Moreover, during rotation the elastomeric ring appreciably moderates the torque peaks that are transmitted to the armature shaft 10. The elasticity of the ring enables the worm drive of the invention to operate more smoothly, with less noise, and, above all, with less wear than worm drives of the prior art.

In accordance with the invention, the coil spring 26 can also be used in conjunction with the elastomeric ring 27 to obtain the cushioning effect. Although the ring is advantageously retained, it can be eliminated and the cushioning obtained solely from the spring 26.

If the teeth clash when trying to mesh the pinion 13 and the spur gear 34, the driver 16 is pushed, by means of the starting lever 31, the collar 30, and the spring 32, still farther leftward until the elastomeric ring 27 presses against the coupling member 19. The driver 16, the coupling member 19, and the pinion 13 are rotated by the coarse thread 15, as a consequence of which the teeth of the pinion and the spur gear come into mesh in many cases before the starter motor is turned on.

If the pinion 13 is not sufficiently rotated, or if two teeth clash edge on edge, the starting lever 31, once the elastomeric ring 27' presses against the coupling member 19, moves the collar 30 leftward, compressing the spring 32, until the starting relay, not shown, closes the starting switch. The starter motor runs and turns the tooth of the pinion 13 past the opposite tooth on the spur gear, so that the force of the compressed spring 32 can push the pinion 13, by means of the coupling member 19 and the driver 16, into mesh with the spur gear 34. The shaft thread 15 screws forward the assembly of 16, 19 and 13 until the pinion strikes the ring stop 35.

When the internal combustion engine starts, the spur gear accelerates the pinion, which now turns faster than the armature shaft 10. The pinion therefore exerts through the backs of the saw teeth 23, and in a direction away from the pinion 13, an axial force on the teeth 22 of the coupling member 19 and on the driver 16. The pinion also exerts an accelerating circumferential force on the driver 16 with respect to the shaft 10. The effect of these two forces and the action of the coarse thread 15 moves the driver to the right, until the retaining ring 28 strikes the face 29 of the pinion flange 24. The acceleration of the pinion 13 reverses the load on the teeth 22 and 23, whereby these teeth, as a consequence of their saw tooth shape, unmesh against the force of the spring, in the manner of an overrunning clutch, until the pinion 13 runs free.

The separation of the teeth 22 and 23 is helped and accelerated by the centrifugal force uncoupler between the pinion 13 and the coupling member 19. As the rotational speed increases, the balls 37 are pressed outwards by the centrifugal force. The resulting force acting on the conical surface 40 of the ring 38 has an axial component that forces the coupling member 19 against the spring 26 so as to unmesh the teeth 22 and 23 quickly and reliably.

it will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a worm drive for starter motors for internal combustion engines, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and described to be protected by Letters Patent is set forth in the appended claims:

1. In a starter arrangement for internal combustion engines, a combination comprising a driven gear on the engine; a driving gear arranged to be put into and out of mesh with said driven gear; a rotary input shaft of a starter motor; drive means movable axially of and operatively connected with said input shaft to perform an angular movement in response to axial movement; shifting means for moving said drive means axially; and coupling means comprising a first member radially spaced from said input shaft and provided on said drive means, a second member movable axially of said drive means and coupled to said first member in operative connection with said driving gear to move the latter angulariy and axially into mesh with said driven gear in response to axial movement of said drive means, and cushioning means between said second member and said drive means for reducing the severity of shocks transmitted to said drive means during startup and acceleration.

2. A combination as defined in claim 1, including an overrunning clutch operatively connecting together said second member and said driving gear; and resilient means for biasing said overrunning clutch into engagement.

3. A combination as defined in claim 2, wherein said driving gear comprises a part adjacent said second member, and said overrunning clutch includes mating teeth on said driving gear part and on said second member.

4. A combination as defined in claim 3, wherein said second member is movable axially of said drive means, and including a centrifugal force uncoupler for helping to disengage said overrunning clutch against the force of said resilient means when said driving gear is accelerated by the engine started up.

5. A combination as defined in claim 4, wherein said centrifugal force uncoupler includes an annular ball race in said driving gear part, at least two uniformly spaced balls in said race, and a ring associated with said second member and having a conical surface that is substantially contiguous with said balls and is sufficiently borne upon thereby when the engine accelerates during starting to establish a component of force that acts against said second member to oppose the force of said resilient means.

6. A combination as defined in claim 1, wherein said second member includes a male element and said first member a female element freely accepting said male element so as to permit free axial movement of said second member with respect to said drive means.

7. A combination as defined in claim 1, wherein said drive means comprises a wall extending radially of said input shaft and adjacent said second member, and said cushioning means is held on said wall.

8. A combination as defined in claim 7, wherein said drive means includes a sleeve that surrounds a length of said input shaft and is operatively connected thereto.

9. A combination as defined in claim 8, wherein said sleeve is internally threaded and said input shaft length has a thread that meshes with that of said sleeve.

t i t 

1. In a starter arrangement for internal combustion engines, a combination comprising a driven gear on the engine; a driving gear arranged to be put into and out of mesh with said driven gear; a rotary input shaft of a starter motor; drive means movable axially of and operatively connected with said input shaft to perform an angular movement in response to axial movement; shifting means for moving said drive means axially; and coupling means comprising a first member radially spaced from said input shaft and provided on said drive means, a second member movable axially of said drive means and coupled to said first member in operative connection with said driving gear to move the latter angularly and axially into mesh with said driven gear in response to axial movement of said drive means, and cushioning means between said second member and said drive means for reducing the severity of shocks transmitted to said drive means during startup and acceleration.
 2. A combination as defined in claim 1, including an overrunning clutch operatively connecting together said second member and said driving gear; and resilient means for biasing said overrunning clutch into engagement.
 3. A combination as defined in claim 2, wherein said driving gear comprises a part adjacent said second member, and said overrunning clutch includes mating teeth on said driving gear part and on said second member.
 4. A combination as defined in claim 3, wherein said second member is movable axially of said drive means, and including a centrifugal force uncoupler for helping to disengage said overrunning clutch against the force of said resilient means when said driving gear is accelerated by the engine started up.
 5. A combination as defined in claim 4, wherein said centrifugal force uncoupler includes an annular ball race in said driving gear part, at least two uniformly spaced balls in said race, and a ring associated with said second member and having a conical surface that is substantially contiguous with said balls and is sufficiently borne upon thereby when the engine accelerates during starting to establish a component of force that acts against said second member to oppose the force of said resilient means.
 6. A combination as defined in claim 1, wherein said second member includes a male element and said first member a female element freely accepting said male element so as to permit free axial movement of said second member with respect to said drive means.
 7. A combination as defined in claim 1, wherein said drive means comprises a wall extending radially of said input shaft and adjacent said second member, and said cushioning means is held on said wall.
 8. A combination as defined in claim 7, wherein said drive means includes a sleeve that surrounds a length of said input shaft and is operatively connected thereto.
 9. A combination as defined in claim 8, wherein said sleeve is internally threaded and said input shaft length has a thread that meshes with that of said sleeve. 